Angular momentum resolved EELS by energy filtered nanobeam ...

Simon D. Schneider, Cécile Hébert, Guillaume Lucas
Centre Interdisciplinaire de Microscopie Electronique (CIME)
Ecole Polytechnique Fédérale de Lausanne
1015 Lausanne, Switzerland

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Angular resolved EELS
Microscope setup
Data analysis
Conclusion
19.06.2012 Workshop on EELS in materials sciences, Uppsala (S) 2

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Angular resolved EELS
Microscope setup
Data analysis
Conclusion
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Classic
q-resolved
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Bulk silver prepared by twin
jet electropolishing
Zone Axis: [2,1,2]
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Energy Filtered Transmission Electron Microscopy
ΔE
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Evolution of the loss function in the energy
range 0-55 eV as a function of momentum
transfer q in (1 1 1) direction.
A. Alkauskas et al., Ultramicroscopy 110 (2010) 1081–1086
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Angular resolved EELS
Microscope setup
Data analysis
Conclusion
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Challenges:
¡ Energy resolution
¡ Angular resolution
¡ Whole energy plane
¡ Dynamic
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A. Alkauskas et al.
Ultramicroscopy 110 (2010) 1081–1086
0.917 eV
TEM image spectrum,
Sputtered Ag
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Energy filter used as a filter (EFTEM)
Sample
Cross over (chromatic object plane)
Image or diff. pattern on the SEA (achromatic object plane)
Filter
Achromatic image plane
Chromatic image plane (spectrum, energy selecting slit)
Filtered image or diffraction patern
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Size of the diaphragma projected on the sample:
SAA1: 1600 nm; SAA2: 800 nm; SAA3: 320 nm; SAA4: 160 nm
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Energy dispersion is image-couled in diff mode
=> EELS spectrum convolved with SAA
SAA4: 1.9 eV
SAA3: 2.4 eV
SAA2: 5.9 eV
FWHM with 80 cm CL
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TEM mode
NBD mode
TEM OLA3 SAA4
0.917 eV FWHM
NBD without diaphragm
1.015 eV FWHM
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TEM mode
NBD mode
TEM OLA3 SAA4
NBD without diaphragm
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0
G
G/2
Sputtered Ag, 50 nm thick
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Sputtered Ag, 50 nm thick
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CCD camera
Imaging plates
Sputtered Ag, grain orientation [0,0,1]
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Improvement of the technique (summary)
NBED
+ // illum. on small area
+ No aperture needed
beside CLA
- Much more sensitive to
alignment
- More contamination
Imaging Plates
+ High dynamic range
+ No cross-talk
- Manual acquisition and
stack combinaison
- Long scanning time
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Angular resolved EELS
Microscope setup
Data analysis
Conclusion
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B. Schaffer et al., Ultramicroscopy 106 (2006) 1129–1138
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Problems to overcome in EFNBED
¡ Microscope alignment
¡ Angular resolution
¡ Contamination
¡ Energy resolution
¡ Dynamics
¡ Non-isochromaticity
¡ Schaffer correction
¡ Plural scattering
Done
Done
Not yet done
In progress
Done
In progress
In progress
In progress
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Thank you for your attention!
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